Abstract:
Theories of human behavior suggest that people’s decisions to join a group and their subsequent behavior are influenced by perceptions of what is socially normative. In online discussions, where unruly, harassing behavior is common, displaying community rules could reduce concerns about harassment that prevent people from joining while also influencing the behavior of those who do participate. An experiment tested these theories by randomizing announcements of community rules to large-scale online conversations in a science-discussion community with 13 million subscribers. Compared with discussions with no mention of community expectations, displaying the rules increased newcomer rule compliance by >8 percentage points and increased the participation rate of newcomers in discussions by 70% on average. Making community norms visible prevented unruly and harassing conversations by influencing how people behaved within the conversation and also by influencing who chose to join.

From the article:

People who decline to discuss science in public may have good reasons to hold back, given the rate of online harassment. Even as technology companies attempt to respond to unruly behavior after it occurs, volunteer community moderators can also manage and prevent problems for thousands of people in their own communities. Pragmatically, in the r/science community, displaying the rules could prevent >2,000 first-time commenters per month from unruly behavior and increase first-time commenters on scientific topics by >40,000 people per month on average. Experiments by and with real-world communities can evaluate such interventions while also helping social scientists understand how communities form and behave online.

Unregistered members cannot post. Of course many members are anonymous, in the sense that it’s not easy to map their screen name back to the real life identity. PF generally discourages providing personal identifying information.
(PF is the only online discussion board of any sort, including some very politically charged ones, in which I do not post with my real name and hometown).